1. Field of the invention
This invention relates to novel compositions for adhesives sealants and/or coatings containing 3,4-polyisoprenes. More particularly this invention involves curable and non-curable compositions for adhesives sealants and/or coatings containing conventional polymeric components and in addition 3,4-polyisoprenes. A preferred field of application for these compositions is the vehicle industry, especially the automotive industry.
2. Discussion of Related Art
In the manufacture and assembly of automobiles, adhesives sealants and coatings are used for a variety of different purposes. Sealants and adhesives are selected mainly on the base of the following properties:
strength, i.e. shear strength, peel strength PA1 elongation, flexibility PA1 durability PA1 ease of application. PA1 one or more liquid or solid rubbers or elastomers PA1 thermoplastic polymers in the form of finely divided powders PA1 fillers PA1 tackifiers and/or adhesion promoters PA1 plasticizers/extenders PA1 curatives, accelerators, catalysts PA1 stabilizers, antioxidants PA1 rheology improvers.
For coatings, especially underbody coatings, abrasion resistance is an additional criterion. In view of reducing the complexity of car manufacturing and thus reducing manufacturing costs, there is a need for "multifunctional" products, i.e. sealants, adhesives and/or coatings which solve additional problems in addition to their prime function.
Contemporary design of vehicles, machines and appliances involves almost exclusively the use of thin gauge sheet metal. Moving parts and running engines cause vibration of these thin metal structures, which in turn create noise. Numerous methods for noise abatement are known, however, most of these methods require additional manufacturing steps and/or components which have only the function of vibration damping. A prime example of the conventional products for vibration damping are highly filled bitumen pads. These pads have to be extruded, die-cut and shaped in separate steps. Prior to application they frequently have to be heat formed to fit them to non flat structures and then glued to the car body, machine or appliance. Numerous attempts have been made to replace this costly manual procedure by products which can be easily applied by robots. Plastisol formulations serving the dual function of underbody coating (projection against abrasion) and acoustic damping have been described in EP-A-358598, or DE-A-3444863. DE-A-4013318 discloses a two layer underbody coating which performs the dual functions of protecting against abrasion and absorbing noise resulting from impact (stones, gravel, water, etc.). Whereas these products/processes are quite useful for combining the functions of underbody coating and noise abatement, there still remains a need to combine the function of an adhesive and/or sealant with noise reduction. This is particularly desirable for those parts of a car, machine or appliance that do not require a specific coating for protection against abrasion such as trunk and hood lids, doors or fire walls of a car.
Adhesives and sealants for these parts are normally applied early on in production, in the so-called "body shop". Hence, they are applied to the bare, uncleaned metal which is frequently covered with an oil for rust protection. Although plastisols, PVC-plastisols in particular, are used in the body shop, those disclosed in EP-A-358598 or DE-A-3444863 are not suitable as adhesives/sealants for bare metal substrates. The plastisol formulations which are especially designed for bare metal application have poor to no vibration damping properties.
Another class of adhesives/sealants suitable for body shop application are based on rubbers especially vulcanizing compositions based on 1,3-polybutadienes and/or 1,3-polyisoprenes. These preferably contain liquid, low molecular weight polydienes, sulfur and optionally accelerators for sulfur vulcanization. In addition, these formulations may contain solid high molecular weight rubbers, whereby the liquid polydiene(s) and/or the solid rubber may contain functional groups such as hydroxyl groups, carboxylic groups, anhydride groups or epoxy groups. This class of rubber based adhesives/sealants has been the subject of various patent applications, e.g. EP-A-97394, EP-A-309903, DE-A-3834818, DE-A-4120502, DE-A-4122849, EP-A-181441 and EP-A-356715. Although DE-A-4122849 and EP-A-181441 mention a potential use of these compositions for vibration damping and/or sound damping, no reference is made to the efficacy of these compositions for vibration damping, because to the best of applicant's knowledge these materials have not been used for their combined adhesive/sealant and vibration damping properties. The use of 3,4-polyisoprenes for sealants, adhesives and coatings has thus far not been described.